The present invention relates to the field of combustion engines and more specifically to a rotary positive displacement combustor engine. The device employs a scroll compressor and a scroll expander with an orbital shaft displaced between the compressor and expander supplying a means and link for compressing fluids within the scroll compressor and disposing the fluid within the scroll expander within which an ignition source is placed at strategic points within a pair of first isolated zones of the orbiting scroll expander generating a highly efficient process for capturing mechanical and thermal energy from combustion. The scroll expander is operating as a combustor and will herein be referred to as a combustor or scroll combustor.
This invention provides the means to implement thermodynamic power cycles that require constant, or nearly constant, volume combustion. This invention utilizes and extends the application of rotary engine device originally proposed by Leon Creux in U.S. Pat. No. 801,182, “Rotary Engine”. The Creux mechanism functioned as an expander or compressor for engine applications but was limited in that the inventor envisioned and described the expander scroll utilizing a high pressure fluid (steam) introduced into the expander scroll producing mechanical energy from the orbital movement of the expander scrolls. In contrast, this invention can utilize the creation of isolated zones within the scroll expander as the location for combustion and thereby produce both mechanical and thermal energy in a device that achieves near constant volume combustion for engine applications.
The scroll design has been employed in a number of devices that require compression or expansion of fluids, from a review of the prior art material, a significant majority of the innovations have been developed for compressors and relatively few have been for expanders. One of the first attempts to exploit a scroll as an expander for combustion utilized an ignition source located at or near the central chamber of the expander scroll. See U.S. Pat. No. 4,677,949, “Scroll Type Fluid Displacement Apparatus” Youtie, Robert. In the '949 patent, the figures and description describe a compact compressor and expander utilizing a central orbital stator located within a vessel and means for orbiting the stator creating a compressor on one side of the vessel and an expander on the other side of the vessel, separated by the orbital stator. Fluid is compressed on the compressor side of the orbiting scroll with the compressed fluid passing into the expander scroll via a hole located in the face of a circular scroll plate or the rotating shaft. A fuel injector and spark are introduced to the fluid on the expander side of the orbital stator. Combustion is isolated from the compressor by means of a valve device deployed on the expander side of the orbital stator. From the drawings, description and claims of the '949, the combustion location is clearly identified to be taking place within the inner scroll chamber of the expander when the fluid is isolated from the compressor by means of a check valve. Isolating the compressor outlet by means of a check valve in the expander inlet creates several limitations or inefficiencies overcome by the present invention.
When ignition takes place within the inlet chamber of the expander in the '949 and others, the combusted fluid expands very quickly producing a sharp increase in pressure. The increased pressure maintains the check valve closed for a period in which the compressor has to work harder to overcome the pressure created by combustion on the other side of the valve face. As the orbital stator continues to rotate, the high pressure fluid in the inlet chamber is allowed to expand within the scroll expander decreasing the pressure on the valve face. Once pressure within the expander inlet chamber is reduced below the pressure of the compressor outlet, the valve will open and a new volume of clean compressed air is introduced into the inlet chamber of the expander. Even though the expander is allowing the combusted fluid to expand with the expander, residue of combusted fluid will remain in the inlet chamber of the expander with the opening of the valve. The clean air from the compressor outlet mixes with the residue of the combusted fuel and when additional fuel is injected into the inlet chamber of the expander, the fuel and air are diluted by the residual combusted material prior to ignition, reducing the efficiency of the combustion process.
In the present invention, the fuel and air mixture are first isolated from the compressor outlet by the expander walls prior to ignition. The increase pressure of the ignited fuel and air mixture produces torque (force) on the spiral walls of the orbiting expander scroll producing torque or movement of the orbiting scroll expander. The compressor does not have to overcome the pressure of the combusted fluid since it is isolated from the area or point of combustion by the orbiting scroll walls. The compressor is continuously delivering compressed fluid to the inlet chamber of the scroll expander through the hollow shaft and there are no valves or valve systems disposed between the compressor outlet and the expander inlet. The compressed fluid is continuously transferred to the expander where the orbiting expander scroll continuously isolates two separate volumes of fluid per orbit and transfers those volumes away from the intake chamber of the expander scroll prior to combustion. Thermodynamic efficiency is increased when the compressed fluid is isolated from combusted byproducts not apparent in the '949 patent.
Other means for isolating the combustion phase from the compression stage of the thermodynamic cycle are described in several other patents, see U.S. Pat. No. 5,094,205, “Scroll-Type Engine”, Billheimer, James and U.S. Pat. No. 5,293,850, “Scroll Type Rotary Internal Combustion Engine”, Mitsuhiro Nishida, Fukuoka. The descriptions, figures and claims associated with these two patent does not describe a means for exposing the fluid to an ignition source within the expander scroll, once isolated from the intake chamber of the scroll expander.
In the '205 the device, like the '949, uses a compact scroll design that utilizes a central orbiting plate for compression on one side and expansion on the other side. Most of the innovation described by the '205 patent involves the unique means in which the shared scroll plate is orbited within a central chamber. Fluid, once compressed by the scroll compressor is delivered to the expander side of the internal scroll plate by means of a hole placed near the center of the orbiting scroll plate—once fluid is transferred to the other side of the scroll plate (the expander side), the orbiting plate continues to rotate until a vein of the fixed plate compressor covers the hole between the compressor and expander sides of the plate, a spark is timed for igniting the fluid at this point (fixed vein covering the hole) within the inner chamber of the expander scroll and the fluid is combusted. While the '205 does not use a check valve this technique to create isolation of the compressor outlet from the combustor inlet, like the '949 patent, suffers from the same limitations described above in that the combustion in the expander generates a reverse pressure on the compressor outlet causing additional work for the compressor that has to overcome the rapidly increasing pressure in the intake chamber of the expander. Additionally, it appears that the amount of time in which the vein covers the hole disposed between the compressor and expander is insufficient for the combustion to be isolated from the compressor outlet to allow the expander to transfer the combusted mixture from the inlet of the expander. The result of timing the combustion in this manner creates a sequence is in which byproducts created from the combustion process remains in the expander intake chamber or bleeds back into the compressor outlet chamber mixing with clean noncombusted fluid from at the compressor outlet. Sequencing combustion described in the '205 causes the compressor to work more in order to overcome the pressure escalation in the expander and produces mixing of compressed fluid with combustion byproduct prior to combustion.
Another attempt at producing a constant volume combustion machine was identified in U.S. Pat. No. 5,293,850, Nishida. This particular device, like the present invention incorporated a separated scroll compressor and expander with a means for delivering the compressed fluid from the scroll compressor to the intake chamber of the expander. The Nishida design employed a common orbital means for the scroll compressor and expander and a channel (communication passage) for transferring compressed fluid from the outlet of the scroll compressor to the inlet chamber of the scroll expander with a check valve disposed between the compressor and expander within the communication passage. Once the compressed fluid was delivered to the intake chamber of the expander, a spark was timed to ignite the fluid, creating combustion within the intake chamber of the expander and keeping the check valve closed from the compressor. While the design of this machine takes advantage of the dynamic balance achieved in the present invention, the thermodynamic efficiencies are similar to the '949 and the '205 patents and suffer from the same limitations. Combusted fluid within the expander will cause the compressor to work against the closed check valve until pressure is reduced to a sufficient level by the combusted fluids being moved from the intake chamber to the isolated scroll zones within the expander. This extra work is less efficient than the present invention in which the orbital scroll plate of the compressor is assisted by the combustion of the fluid, once isolated by the spiral walls of the scroll expander eliminating any additional pressure produced by combustion for which the compressor will need to overcome. Another shortcoming of this device is the description of the check valve opening once compressor pressure overcomes the combustion pressure being reduced by the expander scroll moving the combusted fluid away from the intake chamber. It appears that this would still result in the mixing of the compressed fluid from the compressor outlet with any low pressure byproducts created during combustion still remaining or not transferred by the scroll expander in the intake chamber of the expander.
It is the objective of the present invention to create a combustion process that more closely resembles the thermodynamic cycle known as the Humphrey cycle. To achieve the efficiencies of the Humphrey cycle, the device enables continuous with positive displacement the combustion process of compressed fluid.
The Humphrey cycle is a thermodynamic process describing the maximum utilization of the Otto cycle (internal combustion engine) and the Brayton cycle (turbine combustion engine), as shown in FIG. 9a-b. All three cycles employ isentropic compression from point 1 to point 2. In the Otto cycle and Diesel cycle, FIG. 9c, this is accomplished from the piston, or rotor, compressing the working fluid adiabatically. In an Otto cycle when the piston is at or near the top of its stroke the fuel air mixture is ignited. The combustion proceeds rapidly at nearly constant volume since the piston motion is slow at the top of its stroke. With this constant volume combustion the pressure rises in proportion with the rise in temperature due to combustion. Similarly, in a Diesel cycle, when the piston is at or near the top of its stroke the fuel is injected into the combustion chamber. The high-temperature from the fluid compression causes auto-ignition of the fuel with the hot fluid (air). As the piston begins to descend and expand the hot combustion products, additional fuel is injected to sustain the pressure and temperature within the cylinder. The Diesel cycle differs from the Otto cycle in that the pressure of combustion is relatively constant since the volume is mechanically expanding during the fuel injection. In an Otto cycle the high-pressure and high-temperature is produced with nearly constant-volume combustion to expand against the piston to produce power.
The Diesel cycle does not produce higher pressures and temperatures from holding the volume constant during combustion, but expands the gas, to produce power, from the mechanical compression generated at the beginning of combustion.
In the Brayton cycle, FIG. 9b, a fluid is compressed to a selected pressure in which heat is added, sometimes through combustion of the fluid. The heated and compressed fluid is delivered to an expansion device so that it can produce work. A portion of this work is used to drive the continuous supply and compression of fluid to the engine, while the remainder of the work represents the net performance of work from the engine. Unlike Otto cycle and Diesel cycle engine concepts, Brayton cycle engines are able to fully expand the heated compressed fluid independent of the level of compression being applied to the incoming fluid. It is important to note that the maximum compression achieved by the heated compressed fluid is the level of compression supplied by the engine. Heating, or combustion, of the fluid is achieved at constant pressure and no pressure increase is achieved during the heating of the fluid. A limitation of the Brayton cycle is that the maximum pressure of the fluid must be mechanically provided by the engine and no pressure increase is provided from fluid heating or combustion. Because the Brayton cycle provides heating at constant pressure, rather than constant volume, more work is consumed by the continuous compression of incoming fluid than other constant volume types of engine cycles.
It is well known that the thermodynamic efficiency of the Otto and Diesel cycles is a function of the compression ratio of the engine. For a given compression ratio, Otto cycle engines are more efficient then Diesel cycle engines. Otto cycle engines tend to require fuels that have rapid burning characteristics in order to realize the advantages of constant-volume combustion. In actual practice these fuels tend to limit Otto cycle engines to lower compression ratios; therefore, high efficiency that is promised with high compression is difficult to achieve. Diesel engines use fuels that are slower burning but can be used at much higher compression ratios.
In actual practice, Diesel engines can achieve efficiency equal to or higher than Otto cycle engines because they can be operated at much higher compression ratio. This higher compression ratio makes the engine heavier which is not desirable in some applications. The additional strength and weight required of Diesel engines to operate at high compression ratios make them more expensive to build and operate. It would be desirable to produce an Otto cycle engine, which is more efficient, with fuels that can handle higher compression ratios. In practice this has not been achieved because both piston-crank and Wankel implementations of Otto cycle engines mechanically limit the duration in which combustion must occur in these engines in order to achieve proper operation. The desired fuels cannot burn as fast as these engines require and these engines cannot be adapted to allow slower combustion without significant performance penalties to the overall output of the engine.
The present invention describes another strategy for achieving constant-volume, combustion that can be implemented into a variety of engine configurations. The invention can be embodied in a configuration that implements widely used thermodynamic internal combustion power cycles like Otto, Diesel, Brayton, or Miller (a more efficient Otto cycle in which the compression cycle is assisted by keeping the intake valve open approximately 20-30% during the compression stroke). The invention can also be embodied in configurations of lesser known, yet more efficient, internal combustion power cycles like the Humphrey cycle, FIG. 9e, or hybrids of these cycles. The invention also allows the engine designer to adapt the combustion duration, and compression ratio, in a manner that will allow the overall engine performance to be optimized. The invention can also be embodied in configurations that are gas-generating cycles for producing hot high-pressure gas and/or thrust. Examples of gas generating cycles for which the invention can be embodied are: the Open Brayton cycle, the open Humphrey, and the Rocket cycle.
Internal combustion engines whether two-cycle or four-cycle and whether following the Otto, Diesel or Miller thermodynamic cycles, are mechanically implemented with either a piston-crank mechanism or Wankel rotor mechanism. Although these mechanisms have many proven benefits and features that enable internal combustion engines, these mechanisms also limit and restrict advancement of internal combustion engines in many ways. Piston-crank and Wankel rotor mechanisms achieve similar functions in that they perform work to compress a volume of fuel-air mixture, hold it for combustion, and then expand the combustion products to produce work.
Geometrically, the volume ratio of compression and expansion of piston-crank or Wankel type engines are somewhat equal based on the particular designs of the various mechanisms. The proportion of compression and expansion can be modified, somewhat, by timing of intake and exhaust ports; however, such adaptations compromises the displacement of fuel-air mixture available to the engine and compromises the overall compression available to the engine. The geometric balance of these mechanisms between compression and expansion limit the ability to completely expand the pressure of combustion; therefore, loss of potential work available.
The present invention does not have a geometric dependence between compression and expansion. The invention captures volumes of fuel-air mixture, initiates combustion, and slowly expands the combustion products. Any level of compression can be applied to an engine implemented with this invention because the compression of the device is achieved external and independent of the invention, or produced as a product of the work during expansion. This is typified by the fact that any level of expansion can be achieved based on the geometry and size of the combustor scroll.
Engines implemented with a piston-crank or Wankel rotor mechanism must achieve combustion during a short period of time as the particular mechanism transitions from compression to expansion of the internal volume. The rate of volume change with respect to combustion, as the mechanism transitions, is rather slow. The crank angle of both mechanisms is often used as a means of measuring duration of various phases of engine cycle events. The duration of crank-angle available for combustion in engines using these mechanisms is only about 30 degrees; that is, after the fuel-air mixture as been compressed, the mixture must be ignited and propagated across the entire mixture before the crank moves another 30 degrees. To achieve this rapid combustion, Otto and Miller cycle engines must be restricted to fuels that will burn quickly. Diesel cycle engines use a slower burning fuel and allow the inefficiencies resulting from longer combustion durations. These restrictions in fuel selection and cycle function result from the limited time available for combustion imposed by these mechanisms.
The present invention is far more adaptable. The invention can accommodate combustion of almost any duration, and since the expansion within the invention is slow, the inefficiencies from expanding combustion are minor for designs or situations that require longer combustion durations. The invention's adaptability and insensitivity towards longer combustion durations removes the design restrictions imposed by piston-crank and Wankel rotor mechanisms. The invention will enable the engine designer to optimize the engine cycle to the combustion duration for the fuels of interest.
Engines implemented with piston-crank and Wankel rotor mechanism are somewhat limited in that both suffer from a conflict between achieving maximum performance and achieving regulated emission quality. The limited combustion duration available to engines using these mechanisms require the temperature of combustion to be increased in order to complete combustion in the time available. Often to achieve maximum power and efficiency, the temperature of combustion must be raised to a level that compromises the quality of emissions. This conflict is a direct result of the constraints imposed by these mechanisms upon the engine design. The fact that the invention is adaptable and insensitive to combustion duration allows combustion temperatures to remain at a rate that can meet or exceed required emission quality.
Piston-crank and Wankel rotor mechanisms are not physically balanced mechanisms in terms of inertial distribution of mass and moments during operation causing a significant amount of vibration and noise. Although much technology has been applied to counter-balance and minimize the vibration of these mechanisms in operation, these mechanisms can't be perfectly balanced. Vibration is a well known problem with engines using these mechanisms. Much weight and complexity of design is required to achieve reliable engines.
In the present invention balance is easily achieved through the use of orbiting scrolls. In one embodiment of the design, the combusting scroll is balanced with an integrated scroll located in the compressor—both scrolls operate in a manner that permits the machine to be more dynamically balanced than piston-crank or Wankel rotor designs. This feature makes the invention suitable for many applications that are negatively affected by the vibration of traditional engines.